This invention relates to numerical control devices for controlling machine tools and industrial robots.
Conventional numerical control devices are controlled by means of the so-called G-codes, which are described, for example, in A. D. Roberts and R. C. Prentice, "PROGRAMMING FOR NUMERICAL CONTROL MACHINES", 1968, McGraw-Hill, New York. The G-codes are fundamentally translation instructions for the linear (G01) or the circular arc movements (G02 or G03) of the machine. Thus, in the case where these movement instruction codes are utilized, the curves which cannot be represented by lines or circular arcs are approximated by means of short line segments. These approximating line segments, which are calculated before the execution of the control, are stored in an exterior storage medium such as an NC tape or a fixed disc. These data on line segments stored in an exterior medium are read out by the numerical control device when the machine tool is to be controlled.
The above conventional numerical control devices, however, has the following disadvantages. When curves that are not representable by lines and arcs are utilized, the curves are first converted into a large amount of short line segment data, which are stored in an exterior storage medium. Thus, an NC tape or a fixed disk of a large capacity is necessary. Further, the large amount of data on the line segments must be read out from the exterior storage medium and transmitted to the numerical control device during the execution of control. As a result, the overhead of the data transmission makes a high-speed control of the machine tool infeasible.